Sealing is a technique as old as civilization. It identifies the owner and indicates the integrity of an object. A written message becomes a document due to a sealing process. Today, sealing and printing techniques are used to avoid unauthorized replication of mass produced objects. However, an increasing economic damage results from forgery due to insufficient security. Security of the sealing process requires that a seal cannot be copied and that the seal stamper or printing plate are held under control. Removal of the seal should lead to its destruction when protection against transfer of seals is needed.
A complex engraved pattern is required to protect against forgery. Nevertheless, every structure created by human beings can be replicated with the necessary skill, information, equipment and time. Typically, the effort to recreate a seal stamper or printing plate will be similar or less than the effort for the production of the original. This has lead to an ever increasing complexity of the sealing process for valuable objects. Holograms can be used as an additional protection.
For authenticating documents and things U.S. Pat. No. 5,145,212 teaches the use of non-continuous reflective holograms or diffraction gratings. Such a hologram or diffraction grating is firmly attached to a surface that contains visual information desired to be protected from alteration. The reflective discontinuous hologram is formed in a pattern that both permits viewing the protected information through it and the viewing of an authenticating image or other light pattern reconstructed from it in reflection. In another specific authentication application of this US Patent a non-transparent structure of two side-by-side non-continuous holograms or diffraction patterns, each reconstructing a separate image or other light pattern, increases the difficulty of counterfeiting the structure.
PCT application WO87/07034 describes holograms, including diffraction gratings, that reconstruct an image which changes as the hologram is tilted with respect to the viewer and in a manner that images reconstructed from copies made of the hologram in monochromatic light do not have that motion.
In UK Patent Application GB 2 093 404 sheet material items which are subject to counterfeiting have an integral or bonded authenticating device which comprises a substrate having a reflective diffractive structure formed as a relief pattern on a viewable surface thereon and a transparent material covering the structure. Specified grating parameters of the diffractive structure result in peculiar, but easily discernable, optical colour properties that cannot be copied by colour copying machines.
U.S. Pat. No. 4,661,983 describes a random-pattern of microscopic lines or cracks having widths in the order of micrometers that inherently forms in a dielectric coating layer of an authenticating device incorporated in a secure document. It permits identification of a genuine individual document by comparing read-out line-position information derived by microscopic inspection with read-out digital codes of line-information obtained earlier at the time of fabrication of the document.
The digital data of the random cracks being stored after microscopically inspecting the document these data are used for the fabrication of cracks if the random pattern does not inherently develop.
Although these examples make forging more difficult, they can give no absolute protection. The digital data may be copied and the hologram information may be copied photographically or the hologram may be recreated. Minor deviations of holograms cannot be determined easily, as the extended non-monochromatic illumination within a real-world environment tends to reproduce hologram images with fuzzy shapes and colours.
Forgery of money causes significant economic loss. The advent of high quality copy machines severely threatens many currencies.
Identification documents like passports, identity cards or drivers licenses are used for different purposes, also for governmentally regulated purposes.
Credit cards or corporate badges identify the owner of an account or the employee of a company. In all these cases the document must combine information of the bearer with the authorization information from the issuing organization. An authentication label with personalization on identification documents helps to eliminate the risk to accept an invalid document and with the invention as claimed a machine-based verification is not necessary.
The protection of brand labels has long been a problem. Distribution packages for computer software, in particular, are highly threatened by forgery as the costs for the replication of the package, for example a CD-ROM, are low in comparison with the value of the copied data. An authenticating pattern or authentification label on the data carrier would allow the customer to purchase authorized products and it would allow him to prove the ownership at a legally fabricated product. If all the products of a class or brand were marketed with a personalized authentificating pattern or authentification label, the ownership claim for a stolen object like e.g. an automobile can be verified from an intact pattern or label. A missing pattern or label would indicate manipulation. The exchange of an authentificating pattern or authentification label would not make sense as it requires the possession of an identical product.
A unique pattern or label embedded into a write-once or read-only type data carrier allows to prove the integrity of large sets of coded data. With a reference to the authentificating pattern code or to the authentification label code stored with the data, it is not possible to copy modified data onto an identical data carrier. Attempts to modify data on the original carrier makes no sense as it affects e.g. checksums and other criteria. A forge-proof authentificating pattern or authentification label allows the use of large encoded databases like catasters, patent data bases or financial files as legally approved documents.
All these examples show that equipped with the authenticating pattern or the authentication label objects like money bills, passports, credit cards etc. gain maximum protection against forgery.
Master plates of the authenticating pattern testify the authorization of the label manufacturer.
It is therefore an object of the present invention to provide a light diffracting structure, an authenticating pattern and an authentication label with perceivable parameters where there is no way to directly copy or to recreate the light diffraction structure, the pattern, or the label.